At present, skylights and light tubes used to carry light from a roof to areas within a building are known. Typically the entire inside surface of the tube is equipped with good light reflection. Various types of light collectors are provided at the tube input, usually dome-shaped, and made of resistant plastic material. Diffusers are usually placed at the tube output and are used for light diffusion to illuminate the inside area of the building. Efforts have been made to provide the best possible reflective surface at the inside surface of the light tube. There have also been efforts to develop ways to minimise light loss at the tube input and also at the tube output. As for heat loss, no special modifications to increase heat insulation are provided in the majority of skylights and light tubes of the type described above. Sometimes a thickened material layer and/or a doubled layer is provided at the tube input light collector or at the diffuser. Typically, the roof passage is designed only using a regular sealing material that surrounds the roof entrance point, and/or a flange is created in the light tube part, which serves as the roof passage. For sealing the light tube where it passes through the roof, structures or seals are used which are analogous to those used for sealing smoke-stack passages, ventilation pipelines, or air conduits.
However, an increased risk of imperfect sealing against humidity on the one hand and, on the other, excessive heat loss in general or failure to comply with efficiency standards regarding heat loss, still remain as disadvantages. Addressing these problems, especially the problem of heat loss, by choosing stronger or double walls both for the light collector at the tube input and for the diffuser at the light output from the tube, allows increased light absorption. However, none of the previous arrangements for improving heat insulation provide optimal efficiency, namely for the following reasons. Improved heat insulation at the diffuser still allows heat loss along the tube passage through the building, and so improved heat insulation must be implemented along the whole tube in the building. In this variant, the relatively colder inside area of the tube protrudes more into the building and thus increases the probability of vapour condensation on the lustrous, colder surface of the tube, which, however, worsens its light conduction characteristics significantly. Applying improved heat insulation at the light collector provides a relatively higher portion of the light tube with higher inside temperature, which, although limiting the risk of vapour condensation in the tube, still allows high heat loss because a part of the light tube, for example, between the last heat insulated ceiling and the roof, passes through a relatively colder area.